Electrolytic polishing tool



1965 1.. c. COVINGTON ETAL 3,202,598

ELECTROLYTIC POLISHING TOOL Filed March 22, 1963 INVENTORS. Loren C. Covington Robert L. Powell United States Patent 3,202,598 ELECTROLYTIC POLISHlNG TOOL Loren C. Covington, Henderson, and Robert L. Powell,

Las Vegas, Nev., assignors to Titanium Metals Corporation of America, New York, N.Y., a corporation of Delaware Filed Mar. 22, 1963, Ser. No. 267,106 1 Claim. (Cl. 204224) This invention relates to a tool including an electrode useful for electrolytic polishing of the interior of a metal tube.

Electrolytic machining is becoming accepted as a method for removing or shaping metal. The process in general involves providing an electrode spaced close to the work piece, flooding the space between the work piece and the electrode with an electrolyte while passing electric current between the electrode and the work piece. The work piece is connected to the positive pole of a source of direct electric current and the electrode to the negative pole.

Polishing requires a particularly effective control of an electrolytic machining action since the hills of the surface to be polished must be removed preferentially and with little or no metal removal in the valleys. The electrolyte employed is to some extent corrosive and electrolysis is not easily limited to precise areas. Therefore, considerable difficulty has been encountered in electrolytic machining of metal tubes to provide a smooth, polished interior surface.

It is therefore an object of this invention to provide an improved tool including an electrode for electrolytic polishing of the interior surface of a metal tube. Another object of this invention is to provide a tool including an electrode which, when employed in an electrolytic machining process, can produce a bright polished surface on the interior of a metal tube. These and other objects of this invention will be apparent from the following description thereof and from the annexed drawings, in which:

FIG. 1 is a vertical section of a tool embodying features of this invention.

FIG. 2 is a horizontal section of the tool of FIG. 1 taken along the line 22.

FIG. 3 is a horizontal section of the tool of FIG. 1 taken along the line 33.

Referring now to FIGS. 1, 2, and 3, and particularly to FIG. 1 on which the numerals identifying the various parts are referred to generally reading from top to bot tom, means for supplying electrolyte are shown as flexible hose which may lead from a suitable source of electrolyte (not shown) and this generally will be capable of feeding electrolyte in required amounts under pressure. Hose 10 is attached as by coupling 12 to the'threaded top of an electrically conductive electrolyte supply tube 14. Electrolyte supply tube 14 may advantageously be fabricated of stainless steel which will provide the required electrical conductivity as well as resistance to corrosion by electrolyte. Electrical connector 16 is held in firm electrical contact with supply tube 14 by lock nut 18 which tightens it against the bottom face of coupling 12 as shown.

Also threaded on a top part of supply tube 14 is nut 20 which bears on the top of sleeve 22 which surrounds supply tube 14 and which is preferably fabricated of rigid insulating material such as Bakelite or Micarta. The bottom of sleeve 22 is tapered to engage the correspondingly tapered center hole of sealing ring 24 which is fabricated of insulating material such as polymerized tetraflour ethylene marketed commercially under the trade name Teflon. Sealing ring 24 is of outside diameter to provide a sealing fit when engaged with the in terior wall of a metal tube 26 which is to be polished. The bottom of sealing ring 24 is indented to accommodate the top of electrolyte distributor ring 28 which is welded to the bottom of supply tube 14 as shown and which is provided with a plurality of radial passages 30 terminating in peripheral outlets and communicating centrally with the interior of supply tube 14. Like supply tube 14, distributor ring 28 may advantageously be fabricated of stainless steel for electrical conductivity and corrosion resistance. Distributor ring 28 is additionally provided with a depending shank 32.

The electrode of the tool comprises electrode ring 34' threaded on to distributor ring shank 32. The effective electrode area is actually the outer peripheral surface of electrode ring 34 since the bottom face of electrode ring 34 and shank 32 is insulated as described below. Electrode ring 34 is of electrically conducting and corrosion resistant metal, preferably stainless steel or titanium. It is provided on its upper surface with groove 36 containing 0 ring 38 to provide good sealing between the top of electrode ring 34 and the adjacent surface of distributor ring 28. The bottom of electrode ring 34 is substantially flush with the bottom of shank 32 depending from distributor ring 28. It will be seen that electrode ring 34 is connected to electrolyte supply tube 14 through distributor ring 28 and is disposed below distributor ring 28 considered with respect to the illustration of the tool shown in FIG. 1.

Means are provided to electrically insulate the lower surface of the electrode and this is accomplished in the embodiment illustrated by provision of disc 40 which completely covers the lower faces of electrode ring 34 and shank 32 and which is attached and maintained firmly in position by non-conductive means such as nylon screws 42 which engage threaded holes in electrode ring 34. Disc 40 may, like sealing ring 24, advantageously be fabricated of a fluorinated ethylene plastic such as Teflon.

In operation of the tool of this invention, it is first equipped with sized elements suitable for the particular diameter tube to be polished. Sealing ring 24 is of size to provide sealing engagement with the tube interior sidewall as the tool is passed through the tube. Ordinarily the diameter of sealing ring 24 will be selected to provide the required close sealing fit and additional slight adjustment of its outside diameter may be obtained by turning nut 20 which causes sleeve to exert more or less pressure on the tapered center hole of sealing ring 24, thus causing some expansion or contraction of its external diameter and tightness of fit in the tube. Teflon type material is excellent for fabrication of this element since it is essentially rigid but has some slight flexibility; it is a good electrical insulator, has good corrosion resistance and also presents a slippery surface which is in a sense self-lubricating when passing through the interior of the tube 26 to be polished. A good liquid seal between sealing ring 24 and tube 26 side wall is necessary to prevent electrolyte flowing out of outlets 30 in distributor ring 28 from flowing up the tube. Electrolyte is thereby caused to flow between electrode ring 34 and the side wall of tube 26 to insure proper electrolytic action.

Electrode ring 34 is of an outside diameter so that there is clearance all around it at the beginning of the operation of between about 0.002 and 0.01 inch. This provides necessary close spacing between electrode ring 34 and tube 26 sidewall. Proper alignment and centering of electrode ring 34 is maintained by adjacent sealing ring 24 which acts also as a centering and spacing element in addition to its sealing function.

With the tool set up as described above, a source of direct electric current is connected, the negative pole connected to connector 16 and thus connected through metallic electrolyte supply pipe 14 and distributor ring 28 to electrode ring 34, and the positive pole connected by any convenient means (not shown) and which will be understood by those skilled in the art, to the tube 26 to be polished. The current source should be capable of supplying from about 500 to 1000 amperes per square inch of the peripheral area of electrode ring 34.

The tool is then placed in the tube 26 whose interior surface to be polished as shown in FIG. 1 and electrolyte supply hose connected to a source of electrolyte under pressure. The composition of the electrolyte may vary according to various conditions including the metal of tube 26. A suitable electrolyte for example for polishing titanium and stainless steel will be that particularly described and claimed in co-pending application Serial No. 218,499 filed August 22, 1962 by Loren C. Covington and containing about 20% NaCl, 0.4% NaF, 2.8% tartaric acid, 2.8% of 30% H 0 balance water, all percentages being by weight.

With electrolyte flowing under 60 pounds-per square inch pressure at a rate of about 15 gallons per minute, electric power is turned on and the tool is moved through the tube 26 in an upward direction with reference to FIG. 1 and at a speed of /2-inch per minute, these values being typical of polishing the interior of a l /z-inch internal diameter stainless steel tube. The interior surf-ace of tube 26 over which electrode ring 34 has passed will be polished to a smooth, almost mirror finish.

The speed of tool travel, the electric current employed and the electrolyte flow rate are opera-tively interdependent. The current required increases with increase of tool travel speed due to increase in the rate of metal removal and electrolyte flow must be greater at higher tool travel speeds and higher current input to prevent boiling and resultant resistance increase.

Electrolyte flowing downwardly past electrode ring 34 (referring to FIG. 1) may be recovered and recycled as will be apparent.

The tool of this invention promotes efiicient polishing action. The sealing ring 24 keeps the unpolished surface of the tube 26 free from electrolyte thus directing the electrolyte flow from distributor ring past electrode ring 34. Sealing ring 24 also acts to center electrode ring 34 to preserve proper spacing between it and the interior wall of tube 26. The external diameter adjustment of sealing ring 24, by rotation of nut 20, is important to provide the proper sealing fit of this element.

Covering and insulating the bottom face of electrode ring 34, and any other connected bottom face exposed metal surface as the bottom face of shank 32, is also important. This prevents any electrolytic action between these surfaces and the interior of tube 26 which might roughen and etch the polished surface previously obtained. Surprisingly, we have found that flow of the electrolyte over the polished surface does no harm but any stray current as from the lower face of the electrode ring 34 will cause a frosted effect and destruction of the high polish otherwise obtained.

We claim:

A tool including an electrode useful for electrolytic polishing of the interior surface of a metal tube comprising;

(a) an electrically conductive electrolyte supply tube,

(b) means for connecting electric current to said supply tube,

(c) means for supplying electrolyte to the interior of said supply tube,

(d) an electrolyte distributor ring attached to a lower part of said supply tube having peripheral outlets communicating with the interior of said supply tube,

(e) a sealing ring of electrically insulating material surrounding said supply tube,

(f) means including a rigid sleeve surrounding said supply tube and having a tapered lower end engaging the walls of a central hole in said sealing ring and a nut threaded on to said supply tube bearing on the top of said sleeve thereby to adjust the outside diameter of sealing ring by pressure of the lower end of said sleeve against the wall of said central hole in said sealing ring, to provide sealing engagement of the said sealing ring with the interior of a metal tube to be polished,

(g) an electrode including a ring of electrically conductive metal connected to said supply tube and disposed below said distributor ring, and,

(h) electrical insulating means covering the lower face of said electrode.

References Cited by the Examiner UNITED STATES PATENTS 2,707,474 5/55 Wiginton l34166 X FOREIGN PATENTS 137,738 1/60 Russia.

JOHN H. MACK, Primary Examiner. 

